Description:
    Generates a migration of database schema or content.

Example:
    <%= banner_command %> generate migration better_comments -m mymod

    This will create:

        mod/mymod/data/transform/(migration_number)_better_comments.rb


    <%= banner_command %> generate migration better_comments -m mymod --schema

    This will create:

        mod/mymod/data/schema/(migration_number)_better_comments.rb